With the rapid development of the mobile communication technology, the mobile terminal also exhibits diversified development, and the requirement on limiting the mobility of the mobile terminal also appears, i.e. limit the mobile terminal to only work in a specified cell. Currently, there are two common cell locking methods for the mobile terminal.
The first method is to lock the base station ID and system ID. In this method, the number of base stations which can be locked by the mobile terminal is firstly determined, each time the mobile terminal searches out a new base station, then the mobile terminal adds the base station to a base station list, and if the number of the base stations in the base station list reaches a specified number, then the mobile station stops updating the base station list; after having been registered into the base station, the terminal firstly compares to determine whether ID of this base station is already in the base station list, if it is contained in the base station list, then the terminal provides normal service, otherwise the terminal provides limited service.
The second method is to establish duplex channels between the system side and the mobile terminal, in which the system side issues a control command to the mobile terminal so as to configure the subscription list of the terminal, and the mobile terminal continuously monitors the system, reports information according to the requirements, and determines whether or not to provide normal service.
However, during implementation of the present invention, the inventors have found out that the above currently available cell locking methods for a mobile terminal has the following defects: first, the base station has respiratory effect, which means that, in the Code Division Multiple Access (CDMA) system, when the interference signal in a cell is very strong, the actual effective coverage area of the base station will be reduced; and when the interference signal in a cell is very weak, the actual effective coverage area of the base station will be increased. In a word, the respiratory effect exhibits that the coverage radius constricts as the number of users increases. The main reason leading to the respiratory effect is that the CDMA system is a self-interference system, where the increasing of user leads to the increasing of interference and affects the coverage. Due to the existence of respiratory effect, after the signal coverage of the base station becomes larger, the terminal located at the coverage boundary of the base station will be in the subscribed cell, but when the signal coverage of the base station becomes smaller, the terminal will be out of the coverage of the subscribed cell, then the terminal will be in a lock status, thus the service provided by the terminal is limited, and such phenomenon is called ping-pong effect. Secondly, in the abovementioned methods in the related art, although a plurality of base stations can be locked, there is no association among the locked base stations, and it is only judged whether the base station currently providing the service is in the subscribed base station list, if the current base station is not in the subscribed base station list and the number (preset in the terminal in advance) of the subscribed base stations does not reach the specified upper limit, then the base station currently providing the service is added into the subscription list and provides normal service, or the base station currently providing the service is in the subscribed base station list, then normal service will be provided; and if the current base station is not in the subscription list and the subscription list is full, then the terminal only provides limited service. Because there is no restriction relationship among the locked base stations, it leads to that these base stations may form individual islands, which conflicts with the object of locking a cell.